There are plenty of different pinholes you can make! Assuming I am being a little bit less creative and I am making a matchbox pinhole camera lens using a drawing pin in a sheet small sheet from an aluminium can, how can I calculate the aperture and what is it likely to be?
The diameter of a standard pin is 2mm, so the aperture of that is based on the focal length and that should be the distance between the sensor and the lens mount (flange focal distance). So, given that, the math is: FFD/2 assuming a 2mm pinhole. So, on a Canon EF mount with a 44mm flange focal distance, the aperture is f/22.
For formula purposes: